This application claims the priority of Chinese patent application number 201210249620.X, filed on Jul. 18, 2012, the entire contents of which are incorporated herein by reference.
The present invention generally relates to the field of integrated circuit (IC) design technologies and, more particularly, to techniques improving post-layout design during the IC design and fabrication process.
Electronic design automation (EDA) software for integrated circuit (IC) has rapidly increased in importance with the continuous scaling of semiconductor technology. An IC design software often needs various simulation steps to optimize the circuit design parameters, such as pre-layout simulation and post-layout simulation, etc. However, as the IC process technology scales into sub-100 nm, the interconnects become thinner and denser. The performance of nano-scale integrated circuits may be limited because RC delay becomes no less than MOSFET gate delay.
Various techniques have been proposed to simulate backend of line (BEOL) interconnect delay using layout parasitic extraction (LPE) tools during IC circuit design and verification. Currently, during post-layout simulation, the interconnect RC parasitic parameters are extracted by rules based on existing interconnect technology profile (ITP) using the LPE tools. However, in order to assess the parasitic RC variation, extreme ITP parameters value may needed to be used in the current method. Although this method allows IC designers to sign off a design with extreme process conditions, it limits the design margin and may cause overhead in the design.
The disclosed methods and systems are directed to solve one or more problems set forth above and other problems.
One aspect of the present disclosure includes a method for designing an IC chip. The method includes receiving data from a pre-layout design process for the IC chip, routing a plurality of interconnecting wires to connect various devices of the IC chip, and extracting various circuit parameters. The method also includes simulating the IC chip using the extracted various circuit parameters to detect logic or timing error in the IC chip. The extracting the various circuit parameters includes establishing a statistical interconnect technology profile (ITP) file containing at least interconnect parasitic parameters based on correlations of interconnect layer geometric parameter variations.
Another aspect of the present disclosure includes a computer-readable medium storing computer programs. The computer programs can be executed by a computer and perform a method for designing an IC chip. The method includes receiving data from a pre-layout design process for the IC chip, routing a plurality of interconnecting wires to connect various devices of the IC chip, and extracting various circuit parameters. The method also includes simulating the IC chip using the extracted various circuit parameters to detect logic or timing error in the IC chip. The extracting the various circuit parameters includes establishing a statistical interconnect technology profile (ITP) file containing at least interconnect parasitic parameters based on correlations of interconnect layer geometric parameter variations.
Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure.
Reference will now be made in detail to exemplary embodiments of the invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers may be used throughout the drawings to refer to the same or like parts.
Processor 102 may include any appropriate type of general purpose microprocessor, digital signal processor or microcontroller, and application specific integrated circuit (ASIC). Processor 102 may execute sequences of computer program instructions to perform various processes associated with system 100. The computer program instructions may be loaded into RAM 104 for execution by processor 102 from read-only memory 106, or from storage 108. Storage 108 may include any appropriate type of mass storage provided to store any type of information that processor 102 may need to perform the processes. For example, storage 108 may include one or more hard disk devices, optical disk devices, flash disks, or other storage devices to provide storage space.
Display 110 may provide information to a user or users of system 100. Display 110 may include any appropriate type of computer display device or electronic device display (e.g., CRT or LCD based devices). Input/output interface 112 may be provided for users to input information into system 100 or for the users to receive information from system 100. For example, input/output interface 112 may include any appropriate input device, such as a keyboard, a mouse, an electronic tablet, voice communication devices, or any other optical or wireless input devices. Further, input/output interface 112 may receive from and/or send to other external devices.
Further, database 114 may include any type of commercial or customized database, and may also include analysis tools for analyzing the information in the databases. Database 114 may be used for storing information for IC design and fabrication process and other related information. Communication interface 116 may provide communication connections such that system 100 may be accessed remotely and/or communicate with other systems through computer networks or other communication networks via various communication protocols, such as transmission control protocol/internet protocol (TCP/IP), hyper text transfer protocol (HTTP), etc.
During operation, system 100 or, more particularly, processor 102 may perform certain processes to facilitate IC design and fabrication.
As shown in
The pre-layout design 202 may include various design processes for system-level design and register transfer level (RTL) design. After the completion of the pre-layout design 202, functionalities of an IC chip may be determined and the design data, such as the RTL file, is provided to floor planning 204.
The EDA system 100 receives the design data from the pre-layout design process 202 and continues with the floor planning process 204. During floor planning 204, the RTL of the IC chip may be assigned to gross regions of the IC chip, input/output (I/O) pins may be assigned, and large objects (arrays, cores, etc.) may be placed. Further, the RTL may be mapped into a gate-level netlist in the target technology of the IC chip.
During placement 206, the gates in the netlist may be assigned to non-overlapping locations on the die area of the IC chip, and clock signal wiring may be introduced into the design. After the placement 206, routing 208 may be performed. That is, the interconnects or the wires that connect the gates in the netlist are added.
After routing 208, the layout of the IC chip is completed, and the layout may be provided to fabrication process 214, which physically fabricates the IC chip. However, to optimize the performance and power and other constraints, a post-layout optimization process may be iteratively performed with the floor planning 204, placement 206, and routing 208.
For example, the circuit extraction 210 may extract various circuit parameters. The circuit extraction 210 may, based on the connection length and load of the interconnects, extract parasitic resistor/capacitor parameters of every interconnect to obtain corresponding time delay information. The post-layout simulation 212 may put the extracted circuit parameters into the IC circuit and to simulate the circuit to detect any logic or timing error in the circuit.
In certain embodiments, during the circuit extraction 210 and/or post-layout simulation 212, the system 100 may extract certain interconnect technology profile (ITP) parameters, such as interconnect parasitic parameters, based on the correlations of interconnect layer geometric parameters variations.
There are various parasitic capacitances within multi-layer interconnects in an IC chip.
ILD1 is the inter layer dielectric (ILD) between Metal n and Metal n−1 and H1 is its thickness; ILD2 is ILD between Metal n and n+1 which thickness is H2; L, W and T are the length, width and thickness of metal strips in Metal n; S is the space between two metal wire strips. Further, ∈IMD is the permittivity of Inter Metal Dielectric (IMD) material among strips of Metal n. ∈ILD1 is the permittivity of ILD1 and ∈ILD2 is the permittivity of ILD2.
The parasitic capacitances in
C
ILD1∝∈ILD1(W*L/H1) (1)
C
ILD2∝∈ILD2(W*L/H2) (2)
C
coupling
=C
ptop1
+C
ptop2
+C
pbot1
+C
pbot2
+C
IMD1
+C
IMD2 (3)
C
coupling∝∈IMD(T*L/S) (4)
C
total
=C
coupling
+C
ILD1
+C
ILD2 (5)
where CILD2 is the parasitic capacitor between this metal wire and other metal wires on Metal n+1; CILD1 is the parasitic capacitor between this metal wire and other metal wires on Metal n−1; CIMD1 and CIMD2 are parasitic capacitors induced by IMD material between this metal wire and other wires neighbor to it. Cptop1, Cpbot1, Cptop2, Cpbot2 are the fringe coupling capacitors induced by ILD material. CCoupling represents the sum coupling parasitic capacitors between this wire and all the other wires in the same metal layer.
These parasitic capacitor parameters are part of an ITP of the IC chip. Further, when the interconnect parasitic capacitor parameters are extracted by using, for example, a BEOL interconnect parasitic extraction method, the plurality of different predefined layout structures may be used as the references for the actual fabrication process, i.e., the test, measuring, or verification structures.
For example, five types of structures may be predefined for BEOL interconnect parasitic extraction, Massive single layer coupling metal-oxide-metal (MOM) capacitors CMcoupling, Massive MOM capacitors between two layers Cintra-layers, Common Inverter ROROcommon, Inverter RO loaded with CMcoupling ROMcoupling, and Inverter RO loaded with Cintra-layers ROintra-layers. Other structures may also be used.
More particularly, as shown in
Further, as shown in
ROcommon is the Inverter Ring Oscillator (RO) for unit gate delay measurement without any metal RC load. Further, as shown in
Further, as shown in
With the measured capacitance value and known metal wires length and width, not only the actual thickness of metal layers and actual ∈IMD, but also the actual height of ILD and ∈ILD among the two metal layers can be extracted using 3D RC parasitic simulation and 3D structures can be built with geometric parameters of CMcoupling and Cintra-layers's layouts in Synopsys Raphael Interconnect Parasitic RC 3D simulator, as shown in
Further, a typical interconnect technology profile (ITP) file may be generated.
As shown in
Meanwhile, based on the ITP file, LPE software tools (e.g., Synopsys STAR RC) may be used to generate parasitic extraction rules, including the parasitic parameters such as parasitic resistance and parasitic capacitance. The difference between the 3D simulation software and the LPE software may include that: the 3D simulation software is a time-consuming but high-precision numerical simulation, while the LPE software extraction rule generation method the low-accuracy but less time-consuming analytical simulation. To ensure the accuracy of the extraction rules, actual measurement results of the measuring structures and the 3D numerical simulation results are used to extract and correct the process parameter values in the ITP file, and then to measure the process parameters of the metal interconnect layers and single layer coupling capacitance with process calibration and extraction. The ITP file can then be generated.
That is, the prefabricated test/measuring structures' capacitances can be measured to define process induced differences between actual layout dimension values and ideal values, then to calibrate the ITP file for LPE software. Based on the extraction flow, for each measured/test structure, the wafers are scanned to measure each measuring/test structure, the measurement results of the same structure in every different chip are recorded, and the statistical distribution is analyzed to obtain the measured median. The measured median is then used to verify the simulation values of the capacitance of the test structure, and to extract the process parameter values of metal interconnect layers and the dielectric layers among the metal interconnect layers. An accurate ITP file can then be generated. Further, according to extraction rules of the ITP file, the test structures are extracted, and extraction values of metal interconnect layer capacitance can also be obtained.
The difference among the statistical measurement value (median), simulation value, and the extraction value of the large-size parasitic capacitance measurement structure can be reduced through the optimization and adjustment of process parameter values in the ITP file. Table 1 shows the three types of values of the large-size parasitic capacitance of all metal layers based on the optimized typical ITP file. A total of 7 metal interconnect layers are used in the measured structure.
As shown in Table 1, the difference among these values is very small. Especially, the difference between the extract and measured values is below 5%.
Further, the above parasitic capacitance variables may be correlated and thus may be inaccurate when extracted independently or may be unnecessarily limiting the range of the variables. The Principal Component Analysis (PCA) method may used to introduce a validated way to map the correlated random variable parasitic capacitors' values into independent and uncorrelated variables.
For example, the CMcoupling from M2˜M7 can be analyzed and reduced order to several group of independent variables. Assuming VcMcoupling=[CM2coupling, CM2coupling, . . . CM7coupling] is random variable vector, representing the known correlated variable measured capacitance value of CMcoupling in each layers, VCMncoupling(n=2, . . . 7) is the random variable with Gaussian Distribution, μ=[μN2coupling, . . . . μM7coupling] is the mean vector of VCMcoupling and Cv is the covariance matrix of VCMcoupling. Applying PCA, corresponding uncorrelated random variables φ=[φ2, . . . φ7] can be expressed by Equation (6):
φ=A(VCMcoupling−μ) (6)
where, A=[e1, . . . e7] is the orthogonal mapping matrix, ei is the corresponding eigenvector to eigenvalue λi, which satisfies:
λiei=Cvei (7)
The distribution of the random variables φi can be expressed as:
φi=ui+σiτi (i=2,3.7) (8)
where ui is the mean value of φi and σi is the standard deviation of φi.
Thus, the correlated random variable vector VCMcoupling can be expressed with uncorrelated orthogonal normalized random variables
where aij is the ith row, jth column element in the orthogonal mapping matrix A defined in Equation (6).
As shown in Table 2 below, the variable with Gaussian Distributions of 6 kinds of coupling capacitors can be expressed by two principal components with accumulated contribution rate bigger than 95%. It means CMcoupling from M2˜M7 can be reduced order to a vector of two or even one random variables.
For example, the variable capacitance of M2 coupling capacitors VCM2coupling can be expressed as:
V
CM2coupling
=U
M2coupling
+a
11√{square root over (λ1)}ξ1+a12√{square root over (λ2)}ξ2 (10)
where uM2coupling is the mean value of CM2coupling and the typical interconnect technology parameters can be extracted with its value. Moreover, the statistical parameters of ITP variation parameters can also be extracted from the distribution of ξ1 and ξ2.
Thus, based on the above descriptions,
Further, the single coupling capacitance CMcoupling in each metal layer is used to obtain N number of correlated single layer coupling capacitance variables (e.g., CMcoupling M2-M7), where N is an integer greater than 2. A Principal Component Analysis (PCA) method is used to statistically analyze the N number of correlated single layer coupling capacitance variables to convert or map these correlated variables into M number of independent and uncorrelated variables (e.g., CMcoupling M2-M7 Principal component analysis, order reduction).
The M number of independent variables are statistically analyzed to obtain the process parameters and their statistical distributions corresponding to the M independent variables. The process parameters and their statistical distributions, as well as the orthogonal mapping matrix and the eigenvalue (e.g., CMcoupling M2-M7 Parameters & eigenvector, eigen values) are used to express the N number of correlated single layer coupling capacitance variables.
Based on the process parameters and their statistical distributions, as well as the orthogonal mapping matrix and the eigenvalue, corresponding to the M number of independent and un-correlated variables, ITP files including the process parameters and their statistical calculation of the M number of independent and un-correlated variables can be obtained.
Further, in addition to the correlations of the process parameters, the process parameters themselves and variations are also included in the ITP files. For example, the CM1coupling contribution and M1 T/W/S variation parameters are also included, as well as the Cintra-layers contribution and ILD1-ILD6 H variation parameters.
The statistical ITP file, also called the variation-aware ITP file, may then be created to include a variety of ITP files reflecting the correlation of the coupling capacitance of the metal interconnect layers and parameters of each of the metal interconnect layers. Such statistical ITP file can accurately reflect the parasitic capacitance of the metal interconnect layers.
By using the disclosed methods and systems, novel techniques can be developed to perform correlation-considered statistical interconnect parasitic parameters extraction based on, for example, a 40 nm CMOS process technology. Interconnect Technology Profile (ITP) file can be carefully calibrated using 3D simulations based on a comprehensive set of test structures and full mapping tests are performed on these structures to obtain statistical distribution of the layout parasitics. With the statistical data and process information, statistical ITP parameters are extracted using Principal Component Analysis (PCA) method and verified with circuit level verification. The extracted statistical ITP may be accurate and necessary for neon-scale IC process technologies. The issues of the conventional techniques, such as etching damages to the metal film resistor when forming upper copper interconnect to connect the metal film resistor, can be solved and the reliability of the metal film resistor can be substantially increased. Those of ordinary skill in the art can make changes and modifications without departing from the principles and spirits of the present invention.
Number | Date | Country | Kind |
---|---|---|---|
201210249620.X | Jul 2012 | CN | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/CN2012/084898 | 11/20/2012 | WO | 00 | 6/6/2014 |